Attention has been given in recent years to optical disks as recording media capable of recording video and audio data. Optical disks have gained widespread use not only as media that carry contents such as movies but also as recordable media to which users can record desired data. Among the well-known recordable media are DVD-R on which data can be written once per unit area, and DVD-RW to which data can be written repeatedly. While the DVD-Video standard has been known to provide an optical media file format applicable to read-only optical disks, it is also possible to write data to recordable optical media in compliance with this standard.
The DVD-Video standard allows a single recordable disk to accommodate up to 99 titles, each title containing up to 99 chapters (PTT: part of title). When a camcorder (camera and recorder) is used to record data to DVD-R or DVD-RW, a recorded unit ranging from beginning to end of one recording session is recorded as a chapter. Chapters are recorded under a single title that is completed when a specific condition is met, such as when the disk is ejected, when 99 chapters have been recorded or 99 cells have been accumulated within the title, or when the camcorder is switched from moving picture recording mode to still picture recording mode.
When the data recorded in units of chapters is reproduced, there occurs a short but noticeable break after each chapter, i.e., a blank display appears momentarily on the screen. Since each recorded unit generally lasts merely tens to dozens of seconds with the camcorder, getting the ongoing reproduction interrupted at such a frequency is awkward and undesirable.
A seamless connection technique has already been proposed by which to keep video streams connected in an apparently seamless manner during their reproduction (e.g., refer to Japanese Published Unexamined Patent Application No. 2001-352521, FIG. 2).
The conventional technique above involves absorbing discrepancies between video and audio data by supplying additional audio data portions in order to complement the video data when the two kinds of data are multiplexed. For example, according to the NTSC (National Television System Committee) standard, the frame frequency of video data is about 29.97 Hz. If it is assumed that one VOBU (video object unit) equals one GOP (group of pictures) which in turn is equal to 15 frames, then a period of 64 VOBUs is equivalent to 1/29.97×15×64=32.032032 (seconds). Because AC-3 (Audio Code Number 3; Dolby Digital) audio data is processed in increments of 32 milliseconds as AAU (audio access unit), the above-cited technique proposes adding one AAU to every 64 VOBUs and one AAU to every 64,000 VOBUs in order to resolve discrepancies between video and audio data.
However, the conventional technique above fails to fully eliminate the divergences between video and audio data; they tend to accumulate. Furthermore, what the proposed technique offers is merely an attempt to equalize video data temporally with corresponding audio data on an averaging basis. There is still a possibility that discrepancies can occur at points of supposedly seamless connection.